1. Field of the Invention
The present invention relates to an ink jet head cartridge integrally incorporating an ink jet head and an ink tank, and an ink jet recording apparatus on which such cartridge is mounted, and an ink tank.
2. Related Background Art
In the past, in a liquid jet recording apparatus such as an ink jet recording apparatus, generally, the ink was replenished for exchanging an empty ink cartridge by a new cartridge containing a predetermined amount of ink. In this case, if the ink jet recording head itself is cheap, a so-called head/ink-tank integral cartridge wherein a head and an ink tank containing a predetermined amount of ink are integrally formed has been used. In such a recording apparatus, since the recording head can be renewed without fail whenever a predetermined amount of recording is finished (i.e., a predetermined amount of ink is used up) due to the integral design of the ink tank and the head, it is possible to always maintain the good recording quality. And, even if the recording quality is poor, since the ink jet recording head itself can easily be replaced, it is possible to shorten the down time of the recording apparatus. Further, in replenishing the ink, foreign matter can be prevented from entering the ink.
By the way, such an ink cartridge integrally incorporating the head includes the ink tank for storing the ink and for supplying the ink to a discharging portion. Such an ink tank must meet the following functional requirements at least:
(1) preventing the leakage of the ink; PA1 (2) preventing the vaporization of the ink; PA1 (3) storing a predetermined amount of ink and supplying the ink to the discharging portion stably; and PA1 (4) not blocking the discharge of the ink from the discharging portion.
As ink tanks which can meet such functional requirements, an ink tank including an ink bag and an ink tank including an ink absorber therein for applying negative pressure to the ink at the discharging portion have been already known (refer to FIG. 3 of U.S. Pat. No. 4,095,237).
However, in the above ink tank including the ink bag, with respect to the above requirement (4), in order to avoid the blocking of the discharge of the ink from the discharging portion due to the liquid head pressure of the ink, the relative positional relationship between the recording head and the ink tank is constructurally limited, and, further, it is necessary to provide a case for enclosing the ink bag independently from the ink bag in view of the treatment of the ink tank, thus making the ink tank expensive. On the other hand, in the ink tank including the ink absorber which can avoid the blocking of the discharge of the ink from the discharging portion due to the liquid head pressure of the ink, it is practical to provide a vent opening connecting the interior of the ink tank with the atmosphere in order to cope with the change in pressure in the ink tank due to the reduction of the ink amount in the tank (by ink consumption) and/or due to a change in temperature of air in the tank. However, in this case, the ink is liable to be vaporized through the vent opening (this does not meet the above requirement(2)), and, if the ink tank is left in this condition for a long time, vaporization of the ink will occur.
For example, the aqueous ink which has widely been used because it is advantageous in view of safety, generally includes, as its main components, water, dye and a non-volatile solvent. If the volatile component such as water is vaporized, the ratio of the components included in the ink itself will largely change, thus deleterisusly the fixing ability of the ink or paper and/or the recording feature such as the ink density, and further clogging the discharging portion with ink due to the increase in the viscosity of the ink. Further, since the effective available amount of the ink in the ink tank itself is decreased, this structure is economically disadvantageous. In particular, the smaller the capacity of the ink tank or the cartridge of head/ink-tank integral type, the more serious are the disadvantages from the change in composition of the ink and/or the reduction of the ink amount due to the vaporization of the ink.